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Month: May 2015

Intending to enhance my generic heating / cooling controller to read SPI temperature sensors, I purchased an Adafruit MAX31855 module on eBay from a local supplier for about A$26 posted.

The module you might have guessed uses a MAX31855, a Cold-Junction Compensated Thermocouple-to-Digital Converter for K type thermocouple with an SPI interface. The Adafruit module includes a regulator and level translators to use it in a 5V system.

This article describes a simple checkout using a BusPirate V4. Conveniently, the MAX31855 module can be powered from the BusPirate. The thermocouple input is provided by a thermocouple calibrator.

One frequently sees discussions of coupled coils in ham fora, and the advice of the forum experts is commonly sadly lacking.

An example is the thread Impedance matching transformer where the OP is encouraged to make a transformer for 2:1 impedance transformation ratio based simply on turns ratio and a Rule Of Thumb for minimum number of turns.

Lets review a design where two windings of say 10µH and 20µH are wound on a toroidal core. With no flux leakage, the turns ratio would be 1:1.414. The model is a simple one of coupled coils and ignores self capacitance.

100% flux coupling

If there was no flux leakage, the mutual inductance is (10*20)^0.5=14.14µH, and we can build a three component model of the coupled coils along with the intended 100+j0Ω load.

This article reports measurements on a brushless drive used for an RC quadcopter.

Dead time is the time allowed between turning one FET in a half bridge off and the other FET on to ensure that they do not both conduct simultaneously, even for an instant, as very large currents may flow. The dead time specified in ESC configuation is an ‘additional’ delay added over and above circuit delays.

Measuring a stable properly synchronised drive system at minimum speed can expose the effects of insufficient dead time on total drive input current. At minimum speed, very little power is delivered to the propeller and most drive input power is lost in various system losses, so drive current becomes very sensitive to system losses. Continue reading BLDC ESC – effect of insufficient dead time

The Slot.it CS23B is a Porsche supplied as a ‘white’ body only kit which requires assembly and painting work. The body will be an alternate body for a CA23B car.

Above is the body assembly as supplied after priming with Valejo 73.601 acrylic-polyeurathane primer surfacer. The primer was applied to a very lightly scuffed body with an airbrush, it sprayed on well straight from the bottle, levelled nicely, and was no fuss to use it from its convenient squeeze bottle. Continue reading Slot.it CS23B build